1. Field of the Invention
The present invention relates to a light source applicable to an optical communication system based on wavelength division multiplexing (WDM), and more particularly to a light source that can generate light of a wide wavelength band necessary for inducing a spectrum division and wavelength mode locking.
2. Description of the Related Art
A conventional optical communication system based on wavelength division multiplexing (WDM) is a communication system for transmitting and receiving a plurality of optical signals having different wavelengths. The conventional optical communication system communicates with subscribers according to a multiplexing and de-multiplexing operations upon the optical signals, such that communication capability can be easily extended and a high-speed optical communication system can be implemented.
The above-described WDM-based optical communication system multiplexes a plurality of downstream optical signals having different wavelengths to transmit data to the subscribers and outputs a result of the multiplexing. The optical communication system includes a central office (CO) for de-multiplexing the multiplexed downstream optical signals received from the subscribers according to the wavelengths, and a remote node (RN) arranged between each subscriber and the CO for carrying out a relay operation between each subscriber and the CO.
For the above-described WDM-based optical communication system, there have been proposed a plurality of light sources capable of generating optical signals having a single wavelength such as a distributed feedback (DFB) laser, etc., a light source based on spectrum division for dividing light of a wide wavelength band containing a plurality of channels having different wavelengths into a plurality of optical signals according to the wavelengths and using the optical signals according to a result of the division, a mode-locked light source for generating a mode-locked optical signal in response to each externally inputted channel, etc., as light sources for generating optical signals having the different wavelengths.
The spectrum division-based light source and the mode-locked light source described above must include a wideband light source for generating light of a wide wavelength band containing a plurality of channels having different wavelengths, and devices such as an optical waveguide grating or multiplexing filter, etc. for dividing the generated light according to the channels.
The above-described wavelength mode-locked light source is a light source for injecting a preset wavelength channel into a Fabry-Perot (FP) laser and generating an optical signal having the same wavelength as in the channel injected into the FP laser. That is, the above-described wavelength mode-locked light source must include a plurality of FP lasers for generating a mode-locked optical signal, respectively, and a wideband light source for generating wideband light containing a plurality of channels having different wavelengths to be injected into each FP laser.
The spectrum division-based light source uses channels based on the division operation generated from the wideband light source as optical signals, and the wavelength mode-locked light source uses channels generated from the wideband light source so that the FP laser can carry out a wavelength mode-locking operation.
The above-described wideband light source can use a light emitting diode (LED), a super-luminescent diode (SLD), a semiconductor optical amplifier, a microwave pulse light source or an Erbium-doped fiber (EDF) that can generate incoherent light having a wide wavelength band.
However, there are problems in that output power is low and disturbance due to noise, etc. is serious in the conventional wideband light sources. To address the above-described problems, a multi-wavelength light source in which amplification devices such as an EDF, etc. and an FP laser are coupled has been proposed.
There are problems, however, in that the FP laser and the amplification devices such as the EDF, etc. cannot be easily integrated and manufacturing cost increases. Moreover, serious power fluctuation in relation to light of the wide wavelength band according to wavelengths can occur, and the fluctuation phenomenon serves as a factor that can increase relative intensity noise.